In the 5th Generation (5G) communications system, there are three types of session and service continuity modes (SSC mode), which are separately described below. A first mode is to ensure session continuity when a terminated user plane function (TUPF) remains unchanged. As an anchor of a user plane, the TUPF remains unchanged, to ensure session continuity. The TUPF is a last UPF that the user plane is connected to a data network. The TUPF may be considered as a user plane function entity with an anchoring function. A second mode is to maintain session continuity in a specific area. The TUPF remains unchanged in a specific area, but the TUPF changes when user equipment (UE) used by a user moves out of the area. Therefore, session continuity is ensured in the specific area, but session continuity is not ensured outside the area. A third mode is to ensure session continuity when a TUPF changes. In the third mode, when the TUPF changes, session continuity may be ensured in the following manners: A new TUPF is used for a new session initiated by the UE; and a current TUPF is still used for an existing session of the UE. For ease of description, the first mode, the second mode, and the third mode of the SSC mode are respectively referred to as an SSC mode 1, an SSC mode 2, and an SSC mode 3 below.
In an existing solution, for packet data unit (PDU) sessions in the SSC mode 2 and the SSC mode 3, when a session management function (SMF) entity needs to be selected due to an event such as a UE location change (the selected SMF may be a current SMF or a new SMF), an access and mobility management function (AMF) entity performs an SMF selection operation. However, this manner has the following disadvantages: The AMF does not sense information about PDU session management, and if the AMF continues to perform the SMF selection operation, the selected SMF may be improper.